OSPF Convergence

[albertog]

Hello:

We have a network lan/wan configured with OSPF. We have seen that when a cut takes place the time of convergence is around one minute. We would wish to lower the time of convergence and I have been seeing different solutions, to lower the time of the LSAs, the time of hello and Dead timers, or to configuring incremental updates (ISPF). Somebody could recommend some to me of these solutions.??

Kind regards

[smalkeric]

Some changes are immediately detectable. For example, serial line failures that involve carrier loss are immediately detectable by a router. Other failures are harder to detect. For example, if a serial line becomes unreliable but the carrier is not lost, the unreliable link is not immediately detectable. In addition, some media (Ethernet, for example) do not provide physical indications such as carrier loss. When a router is reset, other routers do not detect this immediately. In general, failure detection is dependent on the media involved and the routing protocol used.

http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2003.htm

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper0900aecd80244005.shtml

[jroyster]

Once a neighbor is declared unreachible the convergence is actually very quick...couple seconds depending on how many routers are in the area and size of the OSPF database.

If you want to make it quicker look into lowering your hello and dead timers.

Is this on a LAN or a WAN? because the default timers for each are different.

also the OSPF design guide is pretty decent.

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml